The invention generally relates to pattern definition systems and in particular to a multi-beam pattern definition device for use in a particle-beam processing or inspection apparatus, which is set up to be irradiated with a beam of electrically charged particles and allow passage of the beam through a plurality of apertures thus forming a corresponding number of beamlets, representing a patterned beam to be imaged onto a target. For this task, the pattern definition device comprises a deflection array means having a plurality of blanking openings located such that each of the beamlets traverses one of the blanking openings along a nominal path, and further comprising a plurality of electrostatic deflector electrodes, each of which is associated with a blanking opening and is individually provided with a connecting line for applying an electrostatic potential; in conjunction with an associated counter electrode, each deflector electrode is configured to deflect a beamlet traversing the respective blanking opening by an amount sufficient to deflect the beamlet off its nominal path when applied an activating voltage against the respective counter electrode.
In a particle-beam exposure apparatus employing this kind of pattern definition device, a particle beam is generated by an illumination system and illuminates a pattern definition means having an array of apertures which define a beam pattern to be projected on a target surface. One important application of a particle-beam exposure apparatus of this kind is in the field of nano-scale patterning, by direct ion beam material modification or by electron or ion beam induced etching and/or deposition, used for the fabrication or functionalization of nano-scale devices. Another important application is in the field of maskless particle-beam Lithography, used in semiconductor technology, as a Lithography apparatus wherein, in order to define a desired pattern on a substrate surface, a substrate, e.g., a silicon wafer or mask blank, is covered with a Layer of a radiation-sensitive resist. A desired structure is then exposed onto the photo-resist which is then developed, in the case of a positive resist by partial removal according to the pattern defined by the previous exposure step. The developed resist is used as a mask for further structuring processes such as reactive etching.
The U.S. Pat. No. 5,369,282 (Arai et al.) discloses an electron-beam exposure apparatus using a so called blanking aperture array (BAA) which plays the role of the pattern definition means. The BAA carries a number of rows of apertures, and the images of the apertures are scanned over the surface of the substrate in a controlled continuous motion whose direction is perpendicular to the aperture rows. The rows may be aligned with respect to each other in an interlacing manner so that the apertures form staggered Lines as seen along the scanning direction. Thus, the staggered Lines may sweep continuous Lines on the substrate surface without Leaving gaps between them as they move relative to the substrate, thus covering the total area of the substrate to be exposed. Certainly, if the beam array is scanned over the substrate in a way to fill up the interstitial regions, also a regular array of beams can be used.
An multi-electron beam source with a blanker array is presented by Zhang et al. in “Integrated multi-electron-beam blanker array for sub-10-nm electron beam induced deposition”, J. Vac. Sci. Technol. B 24(6), pp. 2857-2860. That article also presents a discussion of the geometry of the blanking electrodes placed on a blanker array wafer and the associated electric field geometry.
The U.S. Pat. No. 6,768,125 and U.S. Pat. No. 7,084,411 by the applicant/assignee presents a multi-beam maskless lithography concept, dubbed PML2 (short for ‘Projection Mask-Less Lithography #2’), that employs a pattern definition device (PD device) comprising a number of plates stacked on top of the other. U.S. Pat. No. 6,768,125 and U.S. Pat. No. 7,084,411 are hereby incorporated by reference as if set forth in full herein. The PD device comprises at least two different plates having comparably high integration density of apertures and deflectors, namely an aperture plate used to define beamlets permeating the PD device, and a deflector array plate used to individually blank out selected beamlets (‘blanking plate’). Another function, absorbing the majority of heat load imposed by the incoming beam, may be provided by a specific ‘cover plate’ or included the aperture plate which is then placed as a first plate as seen along the direction of the beam. These separate plates are mounted together at defined distances, for instance in a casing.
The aperture plate comprises an array of apertures which define a beam pattern, consisting of beamlets, to be projected on a target surface. Corresponding blanking openings on the blanking plate are associated with said apertures. Said blanking openings are located such that each of the beamlets traverses the blanking opening that corresponds to the aperture defining the beamlet respectively. Each blanking opening is provided with a beamlet deflection means that can be controlled by a blanking signal between two deflection states, namely, a first state (‘switched on’) when the beamlet deflection means has assumed a state in which particles passing through the opening are allowed to travel along a desired path, and a second state (‘switched off’) when the beamlet deflection means is deflecting particles transmitted through the opening off said path.
The US Patent Publication No. 2005/0242302 A1 by the applicant/assignee proposes to form the electrodes around the blanking openings by perpendicular growth employing state-of-the-art electroplating techniques. US Patent Publication No. 2005/0242302 A1 is hereby incorporated by reference as if set in full herein. The beamlet deflection means associated with each aperture comprises a set of beamlet deflection electrodes, usually a pair. Each set has electrodes of different types: a first type are ‘ground electrodes’, which are applied a ground potential, whereas another type, which is called here the ‘active electrodes’, are applied individual potentials in order to switch on or off the respective apertures according to the desired pattern. The ground electrodes are formed so as to have a substantial height over the blanking plate and the active electrodes. This is done in order to provide a better shielding of the blanking deflection means against cross-talking and other unwanted effects such as lens effects incurred by the electrode geometry.
FIG. 12 shows a prior-art embodiment of a PD system 102 in conformance with the U.S. Pat. No. 6,768,125 and US 2005/0242302 A1. The PD system 102 comprises a number of plates 201, 202 which are mounted in a stacked configuration, realizing a composite device whose components serve respective functions. Each of the plates is preferably realized as a semiconductor (in particular silicon) wafer in which the structures have been formed by micro-structuring techniques known in the art. The plates 201, 202 are bonded together at bonding regions 212 in the frame by means of known bonding techniques.
Apertures are located in membranes mb formed by thinned regions of the wafers. Each aperture corresponds to a set of consecutive openings which are defined in said plates; in FIG. 12, two apertures are shown, to represent a large number of apertures forming the aperture field in the membranes mb. The lithography beam lb traverses the plates through this array of apertures.
The first plate in the direction of the incoming beam is an aperture plate 201 (short for ‘aperture array plate’). It absorbs the majority of the impingent lithography beam lb, but the radiation can pass through a number of apertures of defined shape, thus forming a plurality of beamlets A, B; only two apertures and corresponding beamlets are shown in FIG. 12 and the subsequent figures for the sake of clarity. Apart from the task of forming the beamlets, the aperture plate 201 serves to protect the subsequent plate(s) from irradiation damage. For this purpose it may be coated with a resistive layer 210.
Following the aperture array plate 201 downstream, a deflector array plate 202 (DAP; also referred to as blanking array plate in view of their function in the context of the apparatus 100) is provided. This plate serves to switch off the passage of selected beamlets. The DAP has a plurality of openings, which each correspond to a respective aperture of the aperture array plate 201. Each opening is provided with a beamlet deflection means composed of electrodes 220, 221, 220′, 221′ and individually controlled to deflect, if required, particles radiated through the opening off their path.
In the prior-art DAP illustrated in FIG. 12, each beamlet deflection means comprises an active electrode 221, 221′ and a ground electrode 220, 220′ respectively. The electrodes are free-standing with respect to the DAP base membrane. The electrodes may be formed by perpendicular growth employing state of the art techniques.
For instance, beamlet A transgresses the subsequent openings of the pattern definition system 102 without being deflected, since the beamlet deflection means formed by the respective set of beamlet deflection electrodes is not energized, meaning here that no voltage is applied between the active electrode 221 and the associated ground electrode 220. This corresponds to the “switched-on” state of the aperture. Beamlet A passes the pattern definition system 102 unaffected and is focused by the particle-optical system through the crossovers and imaged onto the target. In contrast, as shown with beamlet B, a “switched-off” state is realized by energizing the beamlet deflection means of this aperture, i.e., applying a transverse voltage to the active electrode 221′ with regard to the corresponding ground electrode. In this state, the beamlet deflection means formed by electrodes 220′,221′ deflects the beamlet B off its path. As a consequence the beamlet B will, on its way through the optical system, obey an altered path and be absorbed at an absorbing means provided in the optical system, rather than reaching the target. Thus, beamlet B is blanked. The beam deflection angle is largely exaggerated in FIG. 12; it is, in general, very small, typically 0.2 to 2 thousands of a radian.
The pattern of switched-on apertures is chosen according to the pattern to be exposed on the substrate 17, as these apertures are the only portions of the pattern definition device transparent to the beam lb, which is thus formed into a patterned beam pb emerging from the apparatus.
The PD device comprises generally at least two different plates for comparably high integration density of apertures and deflectors, namely, at least an aperture plate for forming the beamlets (and possibly absorbing the majority of heat load imposed by the incoming beam) and a deflector array plate for selected blanking of beamlets. Moreover, it is conceivable that by using sufficiently complex process flows a PD device could be fabricated also from one plate, e.g., a Silicon-On-Insulator (SOI) Wafer). Highly accurate alignment between the two or more plates and excellent alignment towards the direction of the incoming beam is required.
One approach for a highly integrated deflector array that can be operated as programmable DAP employs electroplated electrodes constructed above a CMOS plate as deflector array plates, as illustrated in FIG. 12. These electrodes are formed vertically with shielding electrodes to reduce cross talk of neighboring apertures. The disadvantage of the electroplating approach with shielding electrodes is related to the limited aspect ratio of the electroplating that can be produced by industrial methods at hand, which considerably limits the achievable integration level.
Another possible way to obtain a highly integrated deflector array operable as programmable DAP that is usable in setups like a PML2, is to produce one CMOS plate accommodating the required circuitry and another plate as a deflector array plate having the electrodes, and then to vertically interconnect the CMOS plate with the deflector array plate by bonding (e.g., eutectic bonding). In this case, for each aperture at least one electrical connection across the plates is required. The vertical interconnection has a major disadvantage connected with the yield problem with the enormous number (up to 1 million) of vertical bonds to be fabricated within a 30 μm×30 μm area space for one bonding, compounded by the fact that the membrane structures have a thickness smaller than 50 μm are highly fragile, rendering the interconnection a delicate process.